1. Field of the Invention
The present invention relates to a projection optical system for projecting an image of a pattern of a reticle onto a substrate, an exposure apparatus including the projection optical system, and an exposure method using the exposure apparatus.
2. Related Background of the Invention
In recent years, high integration and high density in semiconductor integrated circuits have been progressed. In order to narrow the line widths of semiconductor integrated circuits and make circuit patterns more precise, it is desired that the resolutions of photolithography in exposure apparatuses for semiconductor integrated circuit manufacture be further improved. In order to improve the resolutions of photolithography in exposure apparatuses, the wavelengths of exposure light for use in exposure apparatuses have been shortened to those of g-line (436 nm), i-line (365 nm), and KrF excimer laser light (248 nm) until now. Currently, the wavelengths of exposure light is tried to be further shortened to those of exposure light in a wavelength region of shorter than 200 nm, that is, ArF excimer laser light (193 nm) and F2 laser light (157 nm)
Here, in exposure apparatuses, fluorite (CaF2 and the like) having an extremely high light transmittance in a short wavelength region has come to be used as material for some of the optical elements constituting projection optical systems due to the fact that the wavelengths of exposure light have been shortened.
Incidentally, in the above-described exposure apparatuses, it has been known that local flare exists on a wafer, in other words, that flare light reaches the surrounding portion of the point on a wafer where the zero-order light from exposure light reaches. Due to the existence of such local flare, when a pattern having a predetermined line width is formed on a wafer, the formed pattern becomes narrower than the predetermined line width. Accordingly, a manufactured semiconductor device may not have as good performance as desired.
An object of the present invention is to provide a projection optical system in which local flare is limited within an allowable range, an exposure apparatus including this projection optical system, and an exposure method using this exposure apparatus.
The projection optical system of a first aspect of the present invention is a projection optical system for forming an image of a pattern in a first plane onto a second plane using exposure light in a wavelength region of shorter than 200 nm. This projection optical system has a feature in that, when a projection pattern which has a dark pattern and a bright pattern around the dark pattern and which is placed in the first plane is projected onto the second plane, the average illuminance in the area where a projected image of the dark pattern is formed in the second plane is 8 or less, where the illuminance of an image of the bright pattern around the dark pattern in the second plane is set to be 100.
Here, in the projection optical system of the first aspect of the present invention, when a projection pattern which has a dark pattern and a bright pattern around the dark pattern and is placed in the first plane is projected onto the second plane, the average illuminance in the area where a projected image of the dark pattern is formed in the second plane is preferably 5 or less, where the illuminance of an image of the bright pattern around the dark pattern in the second plane is set to be 100. Thus, an image of the first plane (image of the pattern in the reticle plane) can be more precisely formed in the second plane (wafer plane, or image plane of the projection optical system).
Moreover, in the projection optical system of the first aspect of the present invention, when a projection pattern which has a dark pattern and a bright pattern around the dark pattern and is placed in the first plane is projected onto the second plane, the average illuminance in the area where a projected image of the dark pattern is formed in the second plane is more preferably 3 or less, where the illuminance of an image of the bright pattern around the dark pattern in the second plane is set to be 100. Thus, an image of the first plane (image of the pattern in the reticle plane) can be further more precisely formed in the second plane (wafer plane, or image plane of the projection optical system).
According to the projection optical systems of first and second aspects of the present invention, the influence of flare in the second plane can be significantly reduced. Therefore, an image of the first plane (image of the pattern in the reticle plane) can be very favorably and precisely formed in the second plane (wafer plane, or image plane of the projection optical system) using exposure light in a wavelength region of shorter than 200 nm.
Further, the projection optical system of a third aspect of the present invention has a feature in that, when a pattern having a predetermined line width is formed on a substrate placed in the second plane, the change amount in line width of a second pattern relative to the line width of a first pattern is 15% or less, where the first pattern means the pattern which is formed when the surrounding portion of the pattern is a dark portion, and the second pattern means the pattern which is formed when the surrounding portion of the pattern is a bright portion.
According to the projection optical system of the third aspect of the present invention, the change amount in line width between the first pattern which is formed when the surrounding portion of the pattern is a dark portion and the second pattern which is formed when the surrounding portion of the pattern is a bright portion is limited to 15% or less. Therefore, in this projection optical system, the integral of the light intensity of flare light in the dark pattern, the maximum value of the light intensity of the flare light, and the range of a point in the second plane where the flare light at the intensity peak reaches are limited within predetermined ranges. Accordingly, when an image of the first plane is formed in the second plane using exposure light in a wavelength region of shorter than 200 nm, the image of the first plane can be precisely formed in the second plane.
The projection optical system of a fourth aspect of the present invention is a projection optical system for forming an image of a pattern in a first plane onto a second plane using exposure light in a wavelength region of shorter than 200 nm. This projection optical system has a feature in that, when one bright point is located in the first plane, the total energy amount within an annular area in a range apart from the gravity center position of an image of the bright point in the second plane by 1 xcexcm to 4 xcexcm is 1.5 or less, where the total energy amount in the bright point image in the second plane is set to be 100. Thus, an image of the first plane (image of the pattern in the reticle plane) can be more precisely formed in the second plane (wafer plane, or image plane of the projection optical system).
Moreover, in the projection optical system of the fourth aspect of the present invention, which is a projection optical system for forming an image of a pattern in a first plane onto a second plane using exposure light in a wavelength region of shorter than 200 nm, when one bright point is located in the first plane, the total energy amount within an annular area in a range apart from the gravity center position of an image of the bright point in the second plane by 1 xcexcm to 4 xcexcm is preferably 0.8 or less, where the total energy amount in the bright point image in the second plane is set to be 100. According to this projection optical system, an image of the first plane (image of the pattern in the reticle plane) can be further more precisely formed in the second plane (wafer plane, or image plane of the projection optical system).
Further, the projection optical system of a fifth aspect of the present invention has a feature in that, when a pattern having a predetermined line width is formed on a substrate placed in the second plane, the change amount inline width of a second pattern relative to the line width of a first pattern is 15% or less, where the first pattern means the pattern which is formed when the surrounding portion of the pattern is a dark portion, and the second pattern means the pattern which is formed when the surrounding portion of the pattern is a bright portion.
According to this projection optical system of the fifth aspect of the present invention, the change amount in line width between the first pattern which is formed when the surrounding portion of the pattern is a dark portion and the second pattern which is formed when the surrounding portion of the pattern is a bright portion is limited to 15% or less. Therefore, the average illuminance in the area of an image of the dark pattern formed in the second plane and the total energy amount in a predetermined annular area of an image of the bright point formed in the second plane are limited within preferable ranges. Accordingly, when an image of the first plane is formed in the second plane using exposure light in a wavelength region of shorter than 200 nm, the image of the first plane can be precisely formed in the second plane.
Moreover, the projection optical system of a sixth aspect of the present invention is a projection optical system for forming an image of a first plane onto a second plane using exposure light in a wavelength region of shorter than 200 nm. This projection optical system has a feature in that, when a pattern having a predetermined line width is formed on a substrate placed in the second plane, the change amount in line width of a second pattern relative to the line width of a first pattern is 15% or less, where the first pattern means the pattern which is formed when the surrounding portion of the pattern is a dark portion, and the second pattern means the pattern which is formed when the surrounding portion of the pattern is a bright portion.
Here, in the projection optical system of the sixth aspect of the present invention, when a pattern having a predetermined line width is formed on a substrate placed in the second plane, the change amount in line width of a second pattern relative to the line width of a first pattern is preferably 12% or less, where the first pattern means the pattern which is formed when the surrounding portion of the pattern is a dark portion, and the second pattern means the pattern which is formed when the surrounding portion of the pattern is a bright portion. Furthermore, in the projection optical system of the sixth aspect of the present invention, when a pattern having a predetermined line width is formed on a substrate placed in the second plane, the change amount in line width of a second pattern relative to the line width of a first pattern is more preferably 8% or less, where the first pattern means the pattern which is formed when the surrounding portion of the pattern is a dark portion, and the second pattern means the pattern which is formed when the surrounding portion of the pattern is a bright portion.
According to the projection optical system of the sixth aspect of the present invention, the change amount in line width between the first pattern which is formed when the surrounding portion of the pattern is a dark portion and the second pattern which is formed when the surrounding portion of the pattern is a bright portion is limited to 15% or less. Therefore, in this projection optical system, the average illuminance in the area of an image of a dark pattern formed in the second plane and the total energy amount in a predetermined annular area of an image of a bright point formed in the second plane are limited within predetermined ranges. Accordingly, when an image of the first plane is formed in the second plane using exposure light in a wavelength region of shorter than 200 nm, the image of the first plane can be precisely formed in the second plane.
Moreover, if the change amount in line width between the first pattern which is formed when the surrounding portion of the pattern is a dark portion and the second pattern which is formed when the surrounding portion of the pattern is a bright portion is limited to 12% or less, the average illuminance in the area of an image of a dark pattern formed in the second plane and the total energy amount in a predetermined annular area of an image of a bright point formed in the second plane are limited within narrower ranges compared to the case where the change amount in line width is 15%. Accordingly, when an image of the first plane is formed in the second plane using exposure light in a wavelength region of shorter than 200 nm, the image of the first plane can be more precisely formed in the second plane.
Furthermore, if the change amount in line width between the first pattern which is formed when the surrounding portion of the pattern is a dark portion and the second pattern which is formed when the surrounding portion of the pattern is a bright portion is limited to 8% or less, the average illuminance in the area of an image of a dark pattern formed in the second plane and the total energy amount in a predetermined annular area of an image of a bright point formed in the second plane are limited within further narrower ranges than those in the case where the change amount in line width is 12%. Accordingly, when an image of the first plane is formed in the second plane using exposure light in a wavelength region of shorter than 200 nm, the image of the first plane can be more precisely formed in the second plane.
Moreover, the exposure apparatus of a seventh aspect of the present invention has a feature of including an illumination optical system for illuminating a reticle placed in the first plane using exposure light in a wavelength region of shorter than 200 nm, and the projection optical system of anyone of the first to sixth aspects of the present invention for projecting an image of a pattern of the reticle onto a substrate placed in the second plane.
According to this exposure apparatus of the seventh aspect of the present invention, the integral of the light intensity of flare light in a dark pattern, the maximum value of the light intensity of the flare light, and the range of a point in the second plane where the flare light at the intensity peak reaches are limited within predetermined ranges. Therefore, when an image of a reticle is formed on a wafer using exposure light in a wavelength region of shorter than 200 nm, the image of the reticle can be precisely formed on the wafer.
Further, the exposure method of a eighth aspect of the present invention has a feature of including an illumination process for illuminating a reticle placed in the first plane using exposure light in a wavelength region of shorter than 200 nm, and a projection process for projecting an image of a pattern of the reticle onto a substrate placed in the second plane using the projection optical system of any one of the first to sixth aspects of the present invention.
According to this exposure method of the eighth aspect of the present invention, the average illuminance in the area of an image of the dark pattern formed in the second plane and the total energy amount in a predetermined annular area of an image of the bright point formed in the second plane are limited within preferable ranges. Therefore, an image of a reticle can be precisely formed on a wafer using exposure light in a wavelength region of shorter than 200 nm.